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XI-:\V YORK STATE MUSEUM 



plete their prrowth within 16 to 20 cla\s. They emerge from the galls and 

 migrate to birches towaril the end of May or earl\- in- June. The various 

 forms of tliis generation are shown at tignre 173. I hese plant lice li\'e on 

 th(; umlerside of birch leaves, sometimes covering them. I heir young ar(_' 

 met with in tlie vicinity of W^ashington early In June, attaining maturity in 

 about 14 days. This generation has a characteristic appearance in its 

 fourth stage, as shown in figure 174. It is remarkable liecause of its almost 

 perfect mimicr\- of certain Aleurodids. The insects are first pale brownish, 

 changing graduall)' to a dusky or black color. The fourth and fifth gen- 

 erations are essentiall}- identical with the third, the last named attaining 



fig- 175 JI " "■ "1 -^ p !i i s li .1 m .1 m c- 1 1 d i s, 6th generation, secund stage : rt^dorsal view ; 

 *^=dors.il view denuded, showing arrangement of pores, innch en hirged. ( After Pcr- 

 gande, U. S. J>ei)'t Agric. Div. Ent. 'J'ech. Ser, 9, igoi) 



maturity aI)Out the middle of August. It gives birth to a sixth generation 

 which presents an entirely different form, as shown at hgure 175. 



The young are yellowish brown at fu'st, naked, but soon l:)ecome covered 

 with a pruinose or bluish white secretion, gi\ing them a moldy appearance. 

 Later the Ijristh" while iridescent waxy threads develop. This generation 

 accpiires wings, feeds for a time and then forsakes the birch, migrating back 

 to the witch-hazel, where the sexual generation is developed. This latter 

 sometimes becomes exceedingly abundant. The general characters o{ this 

 generation are well illustrated at figure 176. Each female produces from 



